Magnetically controlled optical switches which depend on the Faraday effect are known. That is, the rotation of the plane of polarization of incident linearly plane polarized radiation as it passes through certain materials in a direction parallel to an applied magnetic field, is used to control passage of the radiation through crossed polarizers. The Faraday effect which rotates the plane of polarization depends on the magnetic flux. The degree of rotation per unit path length is in turn proportional to the Verdet constant for any given material. The degree of rotation .theta. in angular minutes is given by: EQU where .theta.=.lambda.lH cos .alpha. (1)
r=the Verdet constant for the material; PA1 l=the length inch of the light path parallel to the magnetic field; PA1 .alpha.=is the angle between the direction of the magnetic field and the light ray.
Faraday rotator materials customarily used in the past, such as flint glass and quartz, for example, have very low Verdet constants; viz., +0.0420 for flint glass and +0.0172 for quartz. These Faraday rotators were, therefore, quite bulky as were the remaining components (polarizers, analyzers etc.,) of the Faraday optical switches.
With the advent of small optical fibers i.e., fibers with core diameters of 100 microns or less, operation from remote sources to remote detectors and electronics has become quite feasible. Miniaturization of the optical switching element thus becomes highly desirable and the bulky Faraday optical light switches constituted of individual polarizing elements, Faraday rotators, etc. are less useful.
A need therefore exists for a small monolithic Faraday effect optical switch in which all of the functional elements are mounted on a single substrate so that essentially all of the switching functions, polarization, Faraday rotation and analysis take place on a single substrate and in a single monolithic switch structure.
Applicant has found that a monolithic Faraday effect optical switch may be constructed by using Faraday rotating layer(s) epitaxially deposited on an optically inactive substrate. A polarizer - analyzer pair is then deposited in a side-by-side arrangement on one side of the substrate over the Faraday rotator layer. A non-magnetic reflecting surface is deposited on the other side of the substrate. Radiation from an input optical fiber is transmitted through the polarizer, element, through the Faraday rotational layer(s) and the optically inactive substrate to the reflecting surface and is reflected back to the analyzer element.
The term "optically inactive" is used in the sense that the substrate is transparent to plane polarized light and does not affect the plane of polarization. The term "radiation" is used in its broadest sense to include electromagnetic energy by in and outside of the visible spectrum.
Such a monolithic switch design with all the functional components on a single substrate is not only very small but has the further advantage that it lends itself to multiple processing, high yield fabrication techniques. That is, a wafer containing Faraday rotational layer(s) deposited on a substrate is subjected to the individual processing steps by which the individual switch elements such as polarizers, analyzers, reflectors etc. for a large number of switches are simultaneously deposited on the surface. Thereafter, the processed wafer is diced to produce a large number of switches.
It is therefore a principal objective of the invention to provide a monolithic, Faraday effect optical switch.
It is a further objective of the invention to provide a monolithic, optical switch in which all of the switch elements are mounted on a single substrate.
Another objective of the invention is to provide a monolithic optical switch which may be readily fabricated by multistep, multi element fabrication techniques for producing many switches simultaneously. Other objectives and advantages of the invention will become readily apparent as the description thereof proceeds.